Comparative analysis of shallow and deep groundwater chemistry, focusing on spatial distribution and assessment of associated health risks at the south-central coastal areas of Bangladesh Open Access

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This study analysed 44 groundwater samples – 30 from shallow (<200 m) and 14 from deep (>200 m) aquifers to assess the drinking water quality in the Barguna district. Parameters such as temperature, electrical conductivity (EC), and pH were measured on-site and major ions (Na, Ca, Mg, K, HCO₃, Cl, and SO₄), As, Fe, and Mn were analysed in the laboratory. The spatial distribution of ions shows higher levels of Ca, Fe, and HCO₃ in shallow tube-wells (STWs) in the north, and elevated levels of Cl, Na, and K in the south. In deep tubewells (DTWs), only HCO₃ is higher compared to STWs. STWs are mainly NaCl type, while DTWs are characterised by Ca-HCO₃ and Na-HCO₃ types. The high EC values and the presence of Cl and Na in STWs indicate brackish to saline water, likely due to ancient saline pockets or saline water intrusion. Meanwhile, the prevalence of HCO₃ in DTWs, along with low Na and Cl, suggests relatively fresh groundwater and not affected by saline intrusion. According to health risk guidelines, shallow groundwater is highly vulnerable to saline and As contamination, which poses significant health risks. Conversely, deep groundwater is considered safe for drinking as it appears free from As contamination.

• Spatial distribution of ions health risks compared to World Health Organization and BDS hydrochemical comparison between shallow and deep groundwater this work will be a baseline study for a coastal district of Bangladesh.